This invention relates to a thermal conductive sheet with conductive foil produced by press bonding a thermal conductive sheet and conductive foil via a primer layer.
A thermal conductive sheet has been generally produced by kneading and forming a material, such as silicone rubber and EPDM, with a thermal conductive filler. Such a thermal conductive sheet is arranged, for example, between a heat-generating electronic component and a heat sink such as a heat dissipation plate or a metal case panel, inside an electric/electronic apparatus to efficiently radiate the heat produced from the electronic component. Therefore, such thermal conductive sheet is in demand and regarded as essential for increasing in speed of the CPUs, for example.
Additionally in the electric/electronic apparatus, external electromagnetic waves may be superimposed on the input/output signals of the electronic component, such as a CPU, as noise, or electromagnetic waves generated by the electronic component itself may be superimposed on the other signals as noise. To protect the electronic component from the influence of the external electromagnetic waves as well as to interfere with the electromagnetic waves generated by the electronic component, conductive foil may be adhered to one side of the above thermal conductive sheet facing the heat sink. Since the conductive foil is generally composed of metal having a high thermal conductivity, presence of the conductive foil between the thermal conductive sheet and the heat sink does not inhibit radiation of the thermal conductive sheet.
During the process of forming the thermal conductive sheet, however, a skin layer is formed on the surface of the thermal conductive sheet, and there is the possibility that this skin layer may interrupt thermal conduction from the thermal conductive sheet to the conductive foil. Although the skin layer can be removed by preprocessing, an uneven surface of the thermal conductive sheet is created. As a result, low adhesion between the thermal conductive sheet and the conductive foil occurs and causes reduction of thermal conductivity. Additionally, when the conductive foil is adhered to the thermal conductive sheet, it is conventional to provide a primer layer between them so as to improve the adhesion. In this case, however, the primer layer may also interrupt the thermal conduction from the thermal conductive sheet to the conductive foil.
An object of the present invention, in the thermal conductive sheet with conductive foil produced by press bonding the thermal conductive sheet and the conductive foil via a primer layer, is to improve thermal conduction from the thermal conductive layer to the conductive foil and thus to improve heat radiation of the thermal conductive sheet with conductive foil.
In order to attain the above object, a thermal conductive sheet with conductive foil of the present invention is produced by press bonding a thermal conductive layer and conductive foil via a primer layer into which a thermal conductive filler in the form of powder, chop, whisker or fiber is mixed.
As a base material of the primer layer, silane compound, titanate compound, alminate compound, caboxylic acid compound and phosphate compound can be used.
Since the primer layer of the present invention has the thermal conductive filler mixed into it, it does not interrupt thermal conduction from the thermal conductive sheet from the conductive foil. The thermal conductive filler is in the form of powder, chop, whisker or fiber, and the thermal conductive layer and the conductive foil are press bonded via the primer layer into which the thermal conductive filler is mixed. Accordingly, the thermal conductive filler, at the time of the press bonding, mechanically destroys a skin layer on the surface of the thermal conductive layer. Therefore, the thermal conduction from the thermal conductive layer to the conductive foil is not hindered by the skin layer at all.
The thermal conductive sheet with conductive foil of the present invention improves thermal conduction from the thermal conductive layer to the conductive foil, eliminating the negative effect of the skin layer and the primer layer, and thus improves heat radiation of the thermal conductive sheet with conductive foil. In addition, because the thermal conductive layer and the conductive foil are press bonded via the primer layer, the thermal conductive sheet with conductive foil of the present invention is superior in strength.
In the present invention, magnetic foil is employed as the conductive foil. Accordingly, the electromagnetic waves shielding effect of the conductive foil is further improved. Therefore, in addition to the previously mentioned advantages, the thermal conductive sheet with conductive foil of the present invention efficiently prevents the external electromagnetic waves from being superimposed on the input/output signals of the electronic component as well as prevents the electromagnetic waves generated by the electronic component itself from being superimposed on the other signals.